Inactivating Mutation in IRF8 Promotes Osteoclast Transcriptional Programs and Increases Susceptibility to Tooth Root Resorption

This is the first study to our knowledge to report a novel mutation in the interferon regulatory factor 8 gene (IRF8 G388S ) associated with multiple idiopathic tooth root resorption, a form of periodontal disease. The IRF8 G388S variant in the highly conserved C-terminal motif is predicted to alter the protein structure, likely impairing IRF8 function. Functional assays demonstrated that the IRF8 G388S mutant promoted osteoclastogenesis and failed to inhibit NFATc1-dependent transcriptional activation when compared with IRF8 WT control. Further, similar to subjects with heterozygous IRF8 G388S mutation, Irf8 +/- mice exhibited increased osteoclast activity in the mandibular alveolar bone surrounding molar teeth. Immunohistochemistry illustrated increased NFATc1 expression in the dentoalveolar region of Irf8 -/- and Irf8 +/- mice when compared with Irf8 +/+ controls. Genomewide analyses revealed that IRF8 constitutively bound to regulatory regions of several thousand genes in osteoclast precursors, and genetic aberration of IRF8 significantly enhanced many osteoclast-specific transcripts. Collectively, this study delineates the critical role of IRF8 in defining osteoclast lineage and osteoclast transcriptional program, which may help in better understanding of various osteoclast-mediated disorders, including periodontal disease. © 2019 American Society for Bone and Mineral Research.